1. Field of the Invention
The present invention relates to a built-in antenna device. More particularly, the present invention relates to a built-in antenna device for an electronic device for communication, realized for contributing to a slim profile of the device and simultaneously securing a wideband.
2. Description of the Related Art
Recently, an electronic device for communication, having various functions and designs emerges. A portable terminal is a representative device of these electronic devices. The portable terminal becomes lightweight and miniaturized in a slim profile and simultaneously diversity of its function stands out even more. Therefore, the portable terminal places an emphasis on reduction of its volume while maintaining or improving its functions in order to meet this desire of a consumer.
Particularly, a folder type terminal and a slide type terminal among the above-mentioned terminals form a mainstream. Recently, a bar type terminal (a so-called ‘smartphone’) where most of the front side serves as a display unit (a touchscreen unit) is brought to the market constantly. As a touch technology develops, a keypad using a separate metal dome is excluded if possible, an electronic device is operated using a touchscreen unit, so that a consumer's various tastes are met.
Particularly, in case of an antenna device of the above-mentioned terminals, an external protrusion type antenna device has been used conventionally. For example, for an antenna device, a rod antenna (or a whip antenna) installed to protrude to the outside of the terminal by a predetermined length, and a helical antenna have been used. In this case, the antenna becomes a most fragile portion that may be destroyed when the terminal drops down, and causes a problem of reducing portability. Therefore, recently, a plate type built-in antenna (a so-called ‘internal antenna’ or an ‘intenna’) mounted inside the terminal is used generally, and efforts are made to improve the characteristic of the built-in antenna device and simultaneously improve an assembly characteristic and productivity.
The plate type built-in antenna device is mounted on a carrier having a predetermined height and provides a distance with respect to a grounding surface of a substrate in the lower side, so that swift radiation performance is realized. However, recently, a technology excluding this carrier and directly installing or forming an antenna device on a Printed Circuit Board (PCB) develops. Furthermore, recently, an antenna device is formed to realize a multiple band (for example, at least two resonance points) using one radiator because a slot shape of the upper surface of the radiator may be formed in various ways so that it is suitable for each desired band. For example, since recently one terminal is realized to use three or more bands such as a Wideband Code Division Multiple Access (WCDMA), a Digital Cellular System (DCS), a Global System for Mobile Communication (GSM), etc., use convenience of the terminal increases.
A most basic antenna device among the above built-in antenna devices is a dipole antenna device operating in a free space. When the dipole antenna device is used together with a metal ground (a grounding surface), it may be realized as a monopole antenna device by an image theory. However, when a radiator is got close to the ground to meet requirements of an antenna device whose profile is low, a capacitive component increases. To reduce this capacitive component, a shorting pin is added to a feeding portion and so an inductive component is increased, so that resonance may be generated in a desired frequency band. This antenna device is a so-called Planar Inverted F Antenna (PIFA). The PIFA is an antenna type used the most as a built-in antenna device of a portable terminal recently.
However, the above-described built-in antenna device should be realized to cover all of various frequency bands. Accordingly, a separate antenna radiator should be used for each relevant band, or even when a single antenna radiator is used, a volume thereof increases.
Therefore, a built-in antenna device capable of contributing slimness of an electronic device by not increasing the volume of the device or reducing the volume while covering all of frequency bands increasing gradually is indispensably required.